Create a stem plot.

Call signatures::

  stem(y, linefmt='b-', markerfmt='bo', basefmt='r-')
  stem(x, y, linefmt='b-', markerfmt='bo', basefmt='r-')

A stem plot plots vertical lines (using *linefmt*) at each *x*
location from the baseline to *y*, and places a marker there
using *markerfmt*.  A horizontal line at 0 is is plotted using
*basefmt*.

If no *x* values are provided, the default is (0, 1, ..., len(y) - 1)

Return value is a tuple (*markerline*, *stemlines*,
*baseline*).

.. seealso::
    This
    `document <http://www.mathworks.com/help/techdoc/ref/stem.html>`_
    for details.


**Example:**

.. plot:: mpl_examples/pylab_examples/stem_plot.py

.. note::
    In addition to the above described arguments, this function can take a
    **data** keyword argument. If such a **data** argument is given, the
    following arguments are replaced by **data[<arg>]**:

    * All positional and all keyword arguments.


